1. Field of the Invention
This invention relates to copying apparatus.
More particularly, the present invention relates to optical copying apparatus.
2. The Prior Art
Optical copiers are widely known, including--but not limited to--electrostatic copiers. All optical copiers have in common that the material to be copied, hereafter called "the original" for convenience, is scanned by a lens system which reproduces an image of the original on an intermediate image carrier. This image is then transferred to a copy carrier (e.g. a sheet of copy paper). All of this is known per se.
Usually, the original is placed onto a transparent support through which it can be scanned. To aid in proper positioning of the original, optical copiers generally have a portion of a frame, of the housing or of some other member, which forms on or adjacent the transparent support an abutment edge against which an edge of the original is placed.
Sometimes, e.g. when a copy is being made in haste or when the operator is simply careless, the edge of the original is not properly placed against the abutment edge, leaving a gap between them. When a copy is then made, this gap will show up on the copy as a dark area (usually strip-shaped) which detracts from the appearance of the finished copy.
To eliminate this problem it has been proposed in German Gebrauchsmuster 6,916,869, to provide on the upper surface of the transparent support a cover strip which extends along the abutment edge. The underside of this strip, i.e. the side facing towards the reproducing lens, has a light-reflecting character approximately equal to that of the most commonly reproduced originals. A part of the original, extending along the edge which is to be placed against the abutment edge, then overlies this strip. Thus, even if there is some gap between the abutment edge and the edge of the original, the gap (which is not usually very wide) will coincide with the strip, and due to the reflectivity characteristic of the strip the gap will not show up on the copy as a dark strip.
This proposal is basically satisfactory. However, further improvements beyond it are desirable for several reasons. The strip is provided on the same surface of the transparent support onto which the original is placed; thus, even though it is thin, the strip does sometimes interfere with the positioning of the original. Furthermore, over a period of time the strip can become damaged by the constant contact with the originals, which will evidently defeat its role of suppressing the occurrence of a dark strip on the copies. Most importantly, however, it is proposed to make the strip as a strip of lacquer or the like which is applied to the transparent support, in order for it to be as thin as possible and to avoid interference with the proper positioning of the original. In these cases, however, it is almost impossible to accommodate the reflection capability of the strip so closely to that of the originals as to avoid the appearance of the undesired dark strip on the copy, if a gap does occur between the edge of the original and the abutment edge of the copier.
Another problem requiring correction--one which is not addressed in the prior art--is that an undesired dark strip will often occur on the copy along the edge of the (reproduced) original which is opposite to the edge that is to be placed against the abutment edge. This can happen if the format of the original does not exactly coincide with the image-delimiting boundaries in the plane of the original (i.e. on or at the transparent support) and in the plane of the intermediate copy carrier, and if the underside of the cover which is normally placed over the original during the copying operation does not have a reflection capability close enough to that of the original, or if this cover has not been placed over the original at all, or (e.g. in the event a thick original is copied, such as a book) the underside of this cover is spaced by a relatively large distance from the surface of the transparent support on which the original rests.